Variable resistance.



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THEODORE W. CASE, SCIPIO, NEW YORK.

VARIABLE RESISTANCE.

1% Drawing.

To all whom it may concern:

Be it known that I, THEODORE W. CASE, a

citizen of the United States of America, and

resident of Scipio, in the county of Cayuga and State of New York, have invented new and useful Improvements in Variable IRe- *sistances, of which the following is a full,

clear, and exact description.

This invention relates to certain improvements in variable resistances, and specifically contemplates a material as an element of an electric circuit, subject to the condition that variations in light produce a corresponding variation in the electrical resistance of the element, thereby effecting a change of current in accordance with variations of light intensity to which the element is exposed.

The object, therefore, of the invention is the production of a material or compound adapted to form a portion of an electric circuit or conductor, the resistance of which diminishes as the intensity of the light to which it is exposed increases.

I have discovered that a material comprising or consisting of a compound of thallium and sulfur can be utilized as a portion of an electric circuit, and that its resistance to the passage of currents through said circuit varies under the influence of light to effect a changeof current in accordance with the intensity of the light rays to which the substance is subjected,-and that a compound of thalliune and sulfur is peculiarly efficient for this purposev and highly sensitive to variation of light intensity due to the fact that the ratio of change or percentage change Of its resistance to the passage of an electric current under variations of light intensity is very great.

An interesting phenomenon of the invention consists in the'fact that the electrical resistance of the material specified is varied by rays of light invisible to the human eye, such variation of current being readily Specification of Letters Patent. Patented APR. 22, 1919 Application filed October 9, 1917. Serial No. 195,653.

may constitute any portion or part of such circuit and when so embodied the compound may be supported in any suitable way for contact and exposure to light rays.

The invention is adapted for and may be applied to various uses, as, for instance, in the Bell photophone, and I, therefore, desire to broadly claim the same without restriction as to the method, manner or condition of use and without limitation as to the addition of any other elements to the material or compound so long as the same do not destroy the utility of the material for this purpose, or any other purpose, and I desire to claim the material for use with either direct, pulsating direct or alternating current. The expression light rays, as used in the specification and claims hereof, is deemed to include both visible and in- ,visible rays.

What I claim is:

1. A resistance element formed of a compound of thallium and sulfur.

. 2. A resistance element formed of a compound comprising thallium and sulfur.

3. A resistance element formed of a material comprising a compound of thallium and sulfur.

4. An electric circuit having a portion supported for exposure to light rays, such portion comprising a compound of thallium and sulfur.

THEODORE W. CASE.

Witnesses:

E. A. THOMPSON, E. I. SPONABLE. 

